fix(reduce): better type and docs for `reduce` (#240)

[Phryxia]

At first I mentionedR but more describing Acc would be better.

• Change type A,B into T, Acc for reduce
• Give proper value name for acc, value instead of a, b
• Add example with explicit seed
• Add @typeParam for tsdoc support

Fixes #240

[ppeeou]

Thank you for your contribution 🙇‍♂️